A variety of devices have been proposed or used for administering drugs transdermally. These devices are generally in the form of a bandage or skin patch that includes a reservoir that contains the drug and a pressure sensitive adhesive component by which the device is attached to the skin. Depending upon the inherent permeability of the skin to a particular drug, the device may also include means for coadministering a percutaneous absorption enhancer or an element, such as a membrane interposed between the reservoir and the skin, that regulates the rate at which the drug or the percutaneous absorption enhancer is administered to the skin.
Release of drug from the transdermal drug delivery device's reservoir typically occurs via diffusion. In such instances, the reservoir is often called a "diffusion matrix". These matrices are composed of a combination of drug-permeable polymer and drug in which the drug is typically dispersed in or encapsulated by the polymer.
The present invention involves a diffusion matrix that uses a reticulated macroporous polymeric foam as a framework for holding a viscoelastic drug-polymer mixture. Porous or foamed elements have been employed in transdermal drug delivery devices in the past but not in the same manner as in the present invention. In particular U.S. Pat. No. 3,797,494 describes the use of a microporous polymer that forms either the drug reservoir matrix or a membrane interposed between a drug reservoir layer and an adhesive layer. The pores of the material are filled with drug permeable liquid and the porous structure of the material is such that its porosity and tortuosity significantly affect the flux of drug through the liquid-filled material. U.S. Pat. No. 4,605,548 describes a transdermal drug delivery device that includes a porous membrane whose pores are filled with a drug-containing liquid that is held in the pores by capillary pressure. Japanese Patent Publication No. J57139011-A describes a matrix consisting of a water swellable porous membrane whose pores are filled with a drug-containing liquid. Finally, several Japanese Patent Publications (see Nos. J58096016-A, J570009714-A, and J5706413-A) describe the use of porous or foam layers as backing or support members in transdermal drug delivery devices. In each instance, the drug is contained in another element, typically in the adhesive layer that contacts the skin.
One shortcoming of prior transdermal drug delivery devices is that when they are removed from the skin the pressure sensitive adhesive tends to remain on the skin rather than staying part of the device. Thus, once removed from the skin, these prior devices would not adhere well to the same site or another site on the skin. This made it impossible or impractical to remove the device for bathing or other reasons. One aspect of the present invention is a transdermal drug delivery device that includes means for restoring the adhesiveness of the basal surface of the device after it has been removed from the skin. Applicant knows of no prior device that has such means.